This invention relates generally to the field of building products of the type used in residential and commercial construction and more particularly to ventilation products which are used to provide ventilation for interior air spaces such as attics and the like.
Virtually all buildings and structural enclosures where human activity takes place require venting of one type or another. The type of venting device employed to provide such venting will depend on the kind of enclosure to be vented and the use to which the vented space is put. For example, bathrooms containing showers typically have active vents with fans to vent moist air and steam from the enclosed bathroom to the outdoors. Kitchens, particularly in restaurants and hotels, similarly have powered vents for removing cooking byproducts such as smoke and steam to the outdoors.
Other interior spaces, such as attics and yard sheds, do not require active venting. However, such enclosures do typically require a passive vent to permit air flow from the enclosure to the atmosphere. Such venting is required, for example, to prevent a buildup of moisture in the space within the enclosure. Passive vents do not include a mechanism for forcing air out of the enclosure. Rather, they simply include a vent structure in the form of an air passageway which allows air to flow through the vent structure.
Whether active or passive, the venting of an interior space of a building enclosure involves making a hole in the building envelope, such as in a roof, and then covering the hole to prevent rain, inclement weather and pests such as birds and animals from entering the enclosure through the hole while at the same time permitting the passage of air into and out of the interior space of the building. While there are many different types and designs of vents, both active and passive vents include generally the same elements, namely, a nailing flange or flashing strip to attach the vent around the hole in the building enclosure, a grill across the hole to keep out unwanted pests while allowing air to pass through and a cap to prevent rain, snow or the like from impinging upon the grill. In active vents there will also be provided a motor driven fan associated with the grill so as to forcibly drive vented air out of the interior space of the building enclosure.
Typically the nailing flange of the vent is made larger than the hole formed in the building envelope, so that the vent can be fixed in place around the hole. For a roof application, the flange is then underlapped and overlapped with for example roofing shingles, to provide for water shedding along the roof past the vent structure.
In the past, roof vents have tended to be made from metal such as galvanized steel or aluminum. Metal has certain advantages including, that it can be formed to exact shapes and according to precise specifications, and depending upon the metal, it is durable in the sense that aluminum, for example, is generally not degraded by exposure to the elements such as rain and sunlight. However, metal can also be difficult to work with, expensive to form and products made from thin metal can be fragile. In a vent, the metal is not required to carry any significant loads. To save material and cost therefore typically quite thin metal is used. Thin sheet metal is easily bent which may assist in forming the vent in the first place, but also means that the formed product can be damaged easily.
Quite simply the thin sheet metal will be easy to bend into and then possibly out of the desired shape. Any bumps or knocks which typically occur during shipping can leave dents in the surface of the vent cover which then make the vent unacceptable to customers. Alternately the base may become misshapen and twisted making it difficult to attach the device onto a planar surface of the building enclosure such as a roof. Sheet metal vents therefore tend to suffer from very high return rates due to delivery or other incidental damage. Also, installers may desire a water proof seal between the flanges and the roofing shingles and thus installers tend to use various sealant compounds to seal the edges of the flange to the surface on top which the vent is being fixed, in addition to nailing.
More lately, plastic roof vents have been developed which are typically made by injection moulding or the like from thermoplastic resins, such as polypropylene. In this manner many units can be made quickly and for less cost than incurred in bending and forming sheet metal. Plastic roof vents are much more durable during transportation, handling and delivery, since any bumps or blows inflicted will tend to be resiliently absorbed by the plastic without any lasting marking or damage. Unlike thin sheet metal the plastic simply does not permanently deform under the ranges of stresses typically incurred in shipping. Therefore, the return rate for plastic vents is advantageously very low.
Plastic roof vents also suffer from various disadvantages however. For example, plastic tends to become brittle as it gets colder. The more brittle the plastic is the more likely it will fail under a sharp impact such as a hammer blow which is likely to occur as the vent is being installed. Most often such vents are secured in place by means of nails or the like, through the nailing flange, meaning that the plastic must be engineered to withstand significant impact blows at low temperatures such as may be found outside during winter. To develop acceptable impact properties requires the use of expensive additives to the plastic resin, which reduces the cost effectiveness of using moulded plastic and can be more difficult to mould properly.
Also, installers may wish to seal the flange of the metal vents to the roof surface with sealants. Many such sealants are incompatible with the most commonly used plastics and sealing of a plastic roof vent by an unskilled installer can lead to failure by reason of the sealant solvents dissolving the plastic flange material that the sealant comes into contact with. Lastly, the coefficient of thermal expansion of the plastic flange is relatively large, meaning that in the case of an increase in temperature (for example during a mid-summer heat wave) the plastic will expand, causing the flange to buckle and raise up the overlying shingles. This promotes a greater possibility of leaks under the roofing shingles. This tendency also encourages the use of sealing compounds in the mistaken belief that this will help to keep the flange closely attached to the underlying roof.
What is desired is a building product or outdoor ventilation product that is durable for shipping and handling and which therefore will not be easily damaged by incidental contact during shipping handling or display. What is also desired is a product which may be inexpensively and quickly mass produced so that the cost of the device is acceptable to purchasers. What is further desired is a product which is dimensionally stable through the range of temperatures typically experienced in outdoor weather to avoid thermally induced buckling and consequential lifting of roofing shingles or the like. What is further desired is a vent that does not require expensive additives to make the plastic cold impact resistant and which is compatible with sealants and their solvents which are typical to the building and in particular to the roofing trades.
Of course the foregoing objects are to be provided in association with a structure which meets the basic requirements of a vent, namely the cap to prevent inclement weather from impinging on the air passage screen; the air passage screen to permit the air to exchange between the interior and the exterior of the building, but to exclude pests and a flange portion which is easily and readily secured around an opening in the building enclosure and which can be readily secured thereto by conventional building techniques, for example, by nailing.
Therefore according to the present invention there is provided a vent for venting a building enclosure, said vent comprising:
a perimeter flange having a nailing means, said nailing means having a coefficient of thermal expansion less than about 3.5xc3x9710xe2x88x925 in./in xc2x0 F., said perimeter flange defining an opening to permit the passage of air therethrough;
a grill structure extending from said perimeter flange and being positioned relative to said opening to permit said air to pass through said grill structure, said grill structure being sized and shaped to prevent unwanted material from passing therethrough into said building enclosure; and
a plastic moulded dent resistant cap sized, shaped and positioned in place above said grill structure to impede precipitation from impinging on said grill structure.
According to a second aspect of the present invention there is also provided a method of making components for a vent for venting a building enclosure comprising the steps of:
making a nailing flange;
inserting said nailing flange into a mold; and
molding an grill structure onto said nailing flange to attach said grill structure to said nailing flange.